Modern signal processing systems call for a variety of complex operations, including correlating, matched filtering, and Fourier transforming. A number of different approaches have been successful in achieving these functions, one of which is a technology based on the propagation of high-frequency acoustic waves on the surface of piezoelectric crystals. The chief advantages of these surface acoustic wave (SAW) devices, compared with alternative technologies, are their simplicity, processing speed, and compactness. Already they have been incorporated into military communication systems, radars, and satellite systems.
Work is currently being done to extend SAW techniques to silicon integrated circuits, thus combining real-time analog processing with complex peripheral circuitry on a single small chip of silicon.
This invention relates to a device capable of executing a high-speed discrete Fourier transform of a signal for the situation in which the signal appears in a parallel format and is read out in a serial format. The device could be used for various signal processing functions, including beamforming, image data compression, etc.
Only one prior art experimental device exists that is capable of performing the above function, and it requires the use of a lithium niobate delay line and a transducer structure to which is bonded an array of diodes fabricated on a silicon-on-sapphire substrate. This prior art embodiment is discussed by Reeder, T. M. and Gilden, M., "Convolution and Correlation by Nonlinear Interaction in a Diode-coupled Tapped Delay Line," Applied Physics Letters, Vol. 22, No. 1, Jan. 1, 1973, p. 8. The prior art device described therein requires separate complicated linearization circuitry to implement a linear discrete Fourier transform.
Prior art which provides useful background information for both the material of this invention and the convolver implemented upon the material comprise the following: (1) Coldren, L. A., "Effect of bias field in a zinc-oxide-on-silicon acoustic convolver", Applied Physics Letters, Vol. 25, No. 9, Nov. 1, 1974, Pp 473-475; (2) Coldren, L. A., "Zinc oxide on silicon memory cells scanned by acoustic surface waves", Applied Physics Letters, Vol. 26, No. 4, Feb. 15, 1975, Pp 137-139; (3) Davis, J. L., "Properties of the MZOS Surface Wave Convolver Configuration N", IEEE Transactions on Electron Devices, Vol. ED-23, No. June 1976, Pp 554-559; and (4) Davis, K. L., "S. A. W. Frequency Synthesis Using a Monolithic ZnO-on-Si Convolver", Electronic Letters, Vol. 12, Sept. 16, 1976, Pp 487-488.